Respiratory Syncytial Virus (RSV), the major etiologic agent of yearly epidemics of lower respiratory tract infections in infants, has been linked to recurrent episodes of wheezing and to the development of airway hyperresponsiveness (AHR) in childhood. Lung inflammation, associated with local production of proinflammatory cytokines and chemokines, plays a crucial role in the immunopathogenesis of acute RSV infection and its long-term morbidity. In studies conducted with the support of the parent grant (AI 40218; PI: Allan R. Brasier; Co-I: Roberto P. Garofalo), we have shown that host gene transcription in RSV-infected epithelial cells occurs via the coordinated activation of the IkB-kinase (IKK) complex, proteolytic degradation of the IkBa inhibitor and nuclear translocation of the nuclear factor (NF) kappa-kB transactivating subunits RelA and p50. We hypothesize that RSV-induced activation of the IKK-NF-kappaB pathway in epithelial cells is the "master switch" that controls the expression of critical networks of inflammatory and immunomodulatory genes in the airway mucosa, leading to lung inflammation and AHR. The aims proposed in this application will apply novel reagents, molecular genetic approaches, and cutting-edge genomics techniques to extend the in vitro cellular studies proposed in our parent grant to the complex in vivo environment of the lung. We will pursue two aims related to this hypothesis: 1. Determine whether selective disruption of NF-kB-regulated gene expression in epithelial cells affects viral clearance, lung inflammation and clinical illness in experimental RSV infection. These studies wall be conducted in our novel transgene mouse, which expresses a regulated, tissue-selective (lung epithelium) dominant negative inhibitor of NF-kappaB under the control of a tetracycline operator system. 2. Characterize the effect of the NEMO-binding domain (NBD), a cell-permeable peptide that blocks IKK activity, on RSV-induced global lung gene expression and AHR. Global lung gene expression, by oligonucleotide-based microarrays, and pulmonary function, by whole body plethysmography, will be studied in RSV-infected BALB/c mice treated intranasally with the NBD peptide. The results of these studies will advance our still limited understanding of the IKK-NF-kappaB pathway in vivo and will contribute to the design of novel pharmacological strategies to treat and/or prevent airway inflammation associated with viral infections.